a) Field of the Invention
This invention relates to a process for preparing high-purity indene from a coal tar fraction and/or a petroleum fraction, and also to high-purity indene.
b) Description of the Related Art
Indene which is contained in coal tar and petroleum residues is used as coumarone-indene resin, modifiers upon production of synthetic resins, and raw materials for various medicines, agrichemicals and other synthetic products. Upon separating and recovering such indene from coal tar and/or petroleum distillation residues by precision distillation, components having boiling points close to indene, for example, phenol, alkylpyridines, benzonitrile, undecane, alkylbenzenes and the like cannot be fully eliminated, thereby making it difficult to recover indene in a highly-purified form. Among these hardly-eliminative components, tar acids such as phenol and cresol and basic components such as alkylpyridines and aniline can be eliminated by washing with an aqueous acid solution and an aqueous alkali solution.
For example, Japanese Patent Publication No. SHO 62-32731 discloses a process for recovering indene from a tar light oil containing indene at a concentration of about 20 wt. %. According to this process, the tar light oil is distilled to obtain a fraction having an indene concentration of 50 wt. % or higher. After successively washing this fraction with an aqueous acid solution and an aqueous alkali solution, the fraction is distilled again.
This process however cannot eliminate neutral components such as benzonitrile, alkylbenzenes and indane. Concerning elimination of benzonitrile among these neutral components, Japanese Patent Application Laid-Open No. HEI 9-301898 discloses a process for the recovery of indene. According to this process, a solid alkali is added to an indene-containing tar light oil, and the resulting mixture is subjected to heat treatment at a temperature of 100.degree. C. or higher. Subsequent to removal of precipitated insoluble matter, distillation is conducted. This process can eliminate benzonitrile and tar acids, but can hardly remove alkylbenzenes, indane and the like. Moreover, this process also requires treatment of waste water and insoluble matter, both of which are produced in the alkali treatment, leading to an increase in the production cost of the indene so obtained. Even a combined application of the above-described conventional techniques is still unable to fully eliminate alkylbenzenes from indene, so that indene available on an industrial scale from such a combined application is limited only to one having a purity as low as 95 to 97 wt. % or so even at the highest.
As has been described above, the conventional processes for eliminating impurities from indene-containing oils can hardly eliminate alkylbenzenes, and for the elimination of all impurities, plural steps are required. None of the conventional processes are therefore satisfactory for the economical preparation of high-purity indene.